Manufacturing device for sic semiconductor substrate

ABSTRACT

A manufacturing device of SiC semiconductor substrates includes a SiC container ( 3 ) in which Si vapor and C vapor are generated in the internal space during the heat treatment, and a high-temperature vacuum furnace ( 11 ) capable of heating the SiC container in Si atmosphere. The device can further be configured such that the SiC container is housed in Si atmosphere and an underlying substrate ( 40 ) is housed in the SiC container, and the high-temperature vacuum furnace is capable of heating with a temperature gradient.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 16/096,475,filed Oct. 25, 2018, which is a 371 of International Application No.PCT/JP2017/016738, filed Apr. 27, 2017, which claims priority ofJapanese Patent Application No. 2016-092073, filed Apr. 28, 2016, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention mainly relates to a manufacturing device of SiCsemiconductor substrates and a method for vapor-phase growth of anepitaxial layer of single crystalline SiC on an underlying substrate.

BACKGROUND ART

As a material for semiconductor waters, silicon carbide (SiC) hasattracted attention in recent years. SiC has high mechanical strengthand high radiation resistance. In addition, SiC shows high valencecontrollability of electrons and holes by adding an impurity and hasfeatures in a wide forbidden band width (e.g., 2.2 eV in 3C-type singlecrystalline SiC), a high breakdown field, and a high saturated driftvelocity of electrons. For such reasons, SiC has been hopefully expectedas a material for next-generation power devices capable of achievinghigh temperature, high frequency, high withstand voltage, and highenvironmental resistance, which cannot be achieved by existingsemiconductor materials. Furthermore, SiC has attracted attention as asubstrate for a light-emitting diode (LED).

A technique for forming an epitaxial layer has been known in a methodfor producing a semiconductor water using SiC. Patent Literatures 1 and2 (PTLs 1 and 2) disclose methods for forming SiC epitaxial layers.

PTL 1 describes that the SiC epitaxial layer is formed by chemical vapordeposition (CVD). In the process of causing the epitaxial layer to grow,a defect generation suppression layer whose growth velocity is reducedto 1 μm/h or less is introduced so that an epitaxial layer with a smallamount of defects can be formed.

Another known technique for causing an epitaxial layer to grow is asfollows. This method for forming an epitaxial layer includes the step ofcausing SiC bulk crystal to grow using a seed crystal addition andsublimation technique and the step of causing liquid-phase growth of anepitaxial layer on a bulk crystal surface. In the step of causing anepitaxial layer to glow, a liquid-phase growth is performed so thatmicropipe defects having propagated from the seed crystal to the bulkcrystal substrate are closed, which achieves formation of a SiCepitaxial layer containing a small amount of micropipe defects.

CITATION LIST Patent Literature

-   PTL1: Japanese Patent Application Laid-Open No. 2007-284298

SUMMARY OF INVENTION Technical Problem

However, the CVD method of PTL 1 has a low growth velocity, and thus,the process period is long especially in a case of forming a relativelythick epitaxial layer. Thus, this method increases manufacturing costs,and therefore, is not suitable for mass production. In a case ofemploying the CVD method, the amount of supply of a source gas variesdepending on the height and place, for example, of the substrate, andthus, the growth velocity can be nonuniform.

In the method using the seed crystal addition and sublimation techniquedescribed above, in the step of causing the epitaxial layer to grow, anelement for increasing solubility of an melted material obtained bymelting SiC is mixed in a silicon melt. Thus, this element might beunintentionally mixed in epitaxial crystal, and different polymorphsmight also be mixed because of a high solvent (carbon) concentration inthe silicon melt. As a result, a failure might occur in forming ahigh-purity epitaxial layer.

The present invention has been made in view of the circumstancesdescribed above, and a primary object of the present invention is toprovide a method for forming a SiC epitaxial layer with high purity in ashort time.

Solution to Problem and Advantageous Effects

Problems to be solved by the present invention are as described above.Solutions to the problems and advantageous effects thereof will now bedescribed.

A first aspect of the present invention provides a vapor-phase epitaxialgrowth method as follows. Specifically, in a state in which a SiCcontainer of a material including polycrystalline SiC is housed in a TaCcontainer of a material including TaC and in which an underlyingsubstrate is housed in the SiC container, the TaC container is heatedwith a temperature gradient such that inside of the TaC container is ata Si vapor pressure. Consequently, C atoms sublimated by etching of theinner surface of the SiC container are bonded to Si atoms in anatmosphere, thereby performing an epitaxial layer growth step of causingan epitaxial layer of single crystalline SiC to grow on the underlyingsubstrate.

In addition, since SiC has high heat resistance, the process temperaturein heating can be increased to about 2000° C., and thus, a high-puritySiC epitaxial layer can be formed in a short time. Furthermore, since amaterial for the epitaxial layer is the SiC container, the epitaxiallayer can be caused to grow uniformly, as compared to, for example, CVDin which a source gas is introduced.

In the vapor-phase epitaxial growth method, a material for theunderlying substrate is preferably an Al compound or a N compound.

Accordingly, with the method of an aspect of the present invention, theunderlying substrate is not limited to SiC, and thus, a versatileepitaxial growth method can be obtained.

In the vapor-phase epitaxial growth method, a material for theunderlying substrate may be SiC, and an off-angle to a <11-20> directionor a <1-100> direction may be 1° or less.

As a result, in a case where the underlying substrate is SiC and theoff-angle is small, a terrace expands, and a high-quality epitaxiallayer of SiC can be easily formed independently of crystallinepolymorphism of the underlying substrate.

In the vapor-phase epitaxial growth method, in the epitaxial layergrowth step, the temperature gradient is preferably 2° C./mm or less.

Thus, with the method of an aspect of the present invention, thepressure of C atoms in the SiC container increases, and thus, anepitaxial layer is allowed to grow sufficiently even with a smalltemperature gradient as described above. As a result, the heater andheating control can be simplified.

In the vapor-phase epitaxial growth method, in the epitaxial layergrowth step, the underlying substrate preferably includes a plurality ofunderlying substrates placed in the SiC container so that the epitaxiallayer is formed on each of the plurality of underlying substrates.

Accordingly, the epitaxial layers can be formed at the same time on theplurality of underlying substrates, and thus, the process can beperformed efficiently. In particular, the use of the method of theaspect of the present invention enables the epitaxial layer to beuniformly formed independently of the position in the SiC container, andthus, quality does not degrade.

Preferably, in the vapor-phase epitaxial growth method, an inner surfaceof the TaC container is preferably Si or a Si compound and heating ingrowth of the epitaxial layer sublimates Si atoms from the inner surfaceof the TaC container so that inside of the TaC container is at a Sivapor pressure.

Accordingly, a labor of an operator can be alleviated, as compared to amethod of placing solid Si or the like in the TaC container. Inaddition, by forming Si or the like over a wide range of the innersurface of TaC, a uniform Si atmosphere can be obtained.

In the vapor-phase epitaxial growth method, crystalline polymorphism ofthe epitaxial layer is preferably 3C-SiC.

Alternatively, in the vapor-phase epitaxial growth method, crystallinepolymorphism of the epitaxial layer may be 4H-SiC or 6H-SiC.

Accordingly, epitaxial layers of various types of crystallinepolymorphism are allowed to grow with advantages of some aspects of thepresent invention.

A second aspect of the present invention provides a method for producinga substrate with an epitaxial layer using the vapor-phase epitaxialgrowth method described above.

With this method, a substrate with a high-purity epitaxial layer can beefficiently produced.

The method for producing a substrate with an epitaxial layer ispreferably as follows. The underlying substrate is made of SiC. Theunderlying substrate is housed in the TaC container withoutinterposition of a SiC container and is heated under a Si vaporpressure, thereby etching the underlying substrate.

In this manner, the TaC container can be used not only for forming theepitaxial layer but also for etching.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A schematic view illustrating a high-temperature vacuum furnacefor use in a heat treatment.

FIG. 2 A cross-sectional structural drawing illustrating a main heatingchamber and a preheating chamber of the high-temperature vacuum furnacein detail.

FIG. 3 Cross-sectional schematic views illustrating a process of causingan epitaxial layer to grow using a TaC container and a SiC container.

FIG. 4 Cross-sectional schematic views for describing atomicarrangements and stacking periods of 3C-SiC single crystal and 4H-SiCsingle crystal.

FIG. 5 A view illustrating an off-angle of a SiC substrate.

FIG. 6 A view illustrating a state in which an epitaxial layer growswith SiC containers disposed inside and outside of a TaC container.

FIG. 7 Micrographs showing a Si surface and a C surface of an epitaxiallayer that has grown with SiC containers disposed inside and outside ofa TaC container.

FIG. 8 Cross-sectional schematic views illustrating four patterns ofheat treatment with different treatment conditions (especially adistance from an underlying substrate to a material).

FIG. 9 A graph showing a relationship between the position of anunderlying substrate and a growth velocity.

FIG. 10 Cross-sectional schematic views illustrating a process ofperforming etching using TaC.

FIG. 11 A cross-sectional schematic view illustrating a state in which3C-SiC epitaxial layers are formed at the same time on a plurality ofunderlying substrates.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings.

First, referring to FIGS. 1 through 3, a high-temperature vacuum furnace11, a TaC container 2, and a SiC container 3 for performing a heattreatment will be described. FIG. 1 is a schematic view illustrating thehigh-temperature vacuum furnace 11 for use in a heat treatment. FIG. 2is a cross-sectional view illustrating a main heating chamber and apreheating chamber of the high-temperature vacuum furnace 11 in detail.FIG. 3 is cross-sectional schematic views illustrating a process ofcausing an epitaxial layer to grow using the TaC container 2 and the SiCcontainer 3.

As illustrated in FIGS. 1 and 2, the high-temperature vacuum furnace 11includes a main heating chamber 21 capable of heating an object (e.g.,an underlying substrate) to temperatures of 1000° C. or more and 2300°C. or less and a preheating chamber 22 capable of preheating the objectto temperatures of 500° C. or more. The preheating chamber 22 isdisposed below the main heating chamber 21, and adjacent to the mainheating chamber 21 vertically (in top-bottom directions). Thehigh-temperature vacuum furnace 11 includes a heat insulating chamber 23disposed below the preheating chamber 22. The heat insulating chamber 23is vertically adjacent to the preheating chamber 22.

The high-temperature vacuum furnace 11 includes a vacuum chamber 19. Themain heating chamber 21 and the preheating chamber 22 are disposedinside the vacuum chamber 19. The vacuum chamber 19 is connected to aturbo-molecular pump 34 serving as a vacuum generator, and a vacuum of10⁻² Pa or less and preferably 10⁻⁷ Pa or less, for example, can beobtained in the vacuum chamber 19. A gate valve 25 is disposed betweenthe turbo-molecular pump 34 and the vacuum chamber 19. Theturbo-molecular pump 34 is connected to an auxiliary rotary pump 26.

The high-temperature vacuum furnace 11 includes a movement mechanism 27capable of moving the object vertically between the preheating chamber22 and the main heating chamber 21. The movement mechanism 27 includes asupport 28 capable of supporting the object and a cylinder 29 capable ofmoving the support 28 vertically. The cylinder 29 includes a cylinderrod 30, and one end of the cylinder rod 30 is coupled to the support 28.The high-temperature vacuum furnace 11 is provided with a vacuum gauge31 for measuring the degree of vacuum and a mass spectrometer 32 formass spectrometry.

The vacuum chamber 19 is connected to an unillustrated stock room forstoring the object through a transport path 65. The transport path 65can be opened and closed by a gate valve 66.

The main heating chamber 21 has a regular hexagon shape incross-sectional plan view, and is disposed in an upper portion of theinternal space of the vacuum chamber 19. As illustrated in FIG. 2, themain heating chamber 21 incorporates a mesh meter 33 as a heater. Afirst multilayer heat reflection metal plate 71 is fixed to a side walland a ceiling of the main heating chamber 21, and is configured toreflect heat of the mesh meter 33 toward the center of the main heatingchamber 21.

In this manner, a layout is made in the main heating chamber 21, inwhich the mesh heater 33 is disposed to surround the object as a heattreatment object, and the multilayer heat reflection metal plate 71 isdisposed outside the mesh meter 33. The mesh meter 33 is configured tohave its width increase toward the top, for example, or is configuredsuch that electric power to be supplied increases toward the top.Accordingly, a temperature gradient can be provided in the main heatingchamber 21. The temperature of the main heating chamber 21 can beincreased to temperatures of 1000° C. or more and 2300° C. or less, forexample.

The ceiling of the main heating chamber 21 is closed by the firstmultilayer heat reflection metal plate 71, whereas a through hole 55 isformed in the first multilayer heat reflection metal plate 71 at thebottom. The object can move through the through hole 55 between the mainheating chamber 21 and the preheating chamber 22 adjacent to the bottomof the main heating chamber 21.

A part of the support 28 of the movement mechanism 27 is inserted in thethrough hole 55. The support 28 has a configuration in which a secondmultilayer heat reflection metal plate 72, a third multilayer heatreflection metal plate 73, and a fourth multilayer heat reflection metalplate 74 are arranged in this order from the top with intervals.

The three multilayer heat reflection metal plates 72 through 74 are eachoriented horizontally and are coupled to one another by a column 35oriented vertically. A receiver 36 is disposed in space sandwichedbetween the second multilayer heat reflection metal plate 72 and thethird multilayer heat reflection metal plate 73 so that the TaCcontainer 2 housing the object can be placed on the receiver 36. In thisembodiment, the receiver 36 is made of tantalum carbide.

An end of the cylinder rod 30 of the cylinder 29 has a flange that isfixed to a lower surface of the fourth multilayer heat reflection metalplate 74. With this configuration, when the cylinder 29 is caused toextend and contract, the object on the receiver 36 can be moved upwardand downward together with the three multilayer heat reflection metalplates 72 through 74.

The preheating chamber 22 is formed by surrounding space below the mainheating chamber 21 by multilayer heat reflection metal plates 76. Thepreheating chamber 22 is configured to have a circular shape incross-sectional plan view. The preheating chamber 22 does not include aheater such as the mesh meter 33.

As illustrated in FIG. 2, a through hole 56 is formed in the multilayerheat reflection metal plate 76 at the bottom of the preheating chamber22. A passage hole 50 is formed in a portion of the multilayer heatreflection metal plate 76 constituting a side wall of the preheatingchamber 22, the portion facing the transport path 65. Thehigh-temperature vacuum furnace 11 also includes an opening/closingmember 51 that can close the passage hole 50.

The heat insulating chamber 23 disposed adjacent to the bottom of thepreheating chamber 22 is defined by the multilayer heat reflection metalplate 76 at the top and by multilayer heat reflection metal plates 77 atthe bottom and the side. A through hole 57 is formed in the multilayerheat reflection metal plate 77 covering the bottom of the heatinsulating chamber 23 so that the cylinder rod 30 can be insertedtherethrough.

The multilayer heat reflection metal plate 77 has a housing recess 58 ata position corresponding to the upper end of the through hole 57. Thehousing recess 58 can accommodate the fourth multilayer heat reflectionmetal plate 74 of the support 28.

Each of the multilayer heat reflection metal plates 71 through 74, 76,and 77 has a structure in which metal plates (made of tungsten) arestacked with predetermined intervals. In the opening/closing member 51,a multilayer heat reflection metal plate having a similar structure isused for a portion closing the passage hole 50.

As a material for the multilayer heat reflection metal plates 71 through74, 76, and 77, any material may be used as long as the material hassufficient heating properties to thermal radiation of the mesh meter 33and has a melting point higher than an ambient temperature. Instead oftungsten used above, a high-melting-point metal material such astantalum, niobium, or molybdenum may be used for the multilayer heatreflection metal plates 71 through 74, 76, and 77. Carbides such astungsten carbide, zirconium carbide, tantalum carbide, hafnium carbide,and molybdenum carbide may be used as the multilayer heat reflectionmetal plates 71 through 74, 76, and 77. Reflection surfaces of themultilayer heat reflection metal plates 71 through 74, 76, and 77 may befurther provided with an infrared reflection film of, for example, goldor tungsten carbide.

Each of the multilayer heat reflection metal plates 72 through 74 of thesupport 28 has a structure in which perforated-metal tungsten plateseach having a large number of small through holes are stacked withpredetermined intervals with the through holes displaced from oneanother.

The number of stacked layers of the second multilayer heat reflectionmetal plate 72 at the uppermost layer of the support 28 is smaller thanthat of the first multilayer heat reflection metal plate 71 of the mainheating chamber 21.

In this state, the object is introduced from the transport path 65 intothe vacuum chamber 19 and is placed on the receiver 36 in the preheatingchamber 22. When the mesh meter 33 is then driven in this state, themain heating chamber 21 is heated to a predetermined temperature of1000° C. or more and 2300° C. or less (e.g., about 1900° C.). At thistime, the driving of the turbo-molecular pump 34 adjusts the pressure inthe vacuum chamber 19 to 10⁻³ Pa or less and preferably 10⁻⁵ Pa or less.

Here, as described above, the number of stacked layers of the secondmultilayer heat reflection metal plate 72 of the support 28 is smallerthan that of the first multilayer heat reflection metal plate 71. Thus,a part of heat generated by the mesh meter 33 is appropriately supplied(distributed) to the preheating chamber 22 through the second multilayerheat reflection metal plate 72 so that the object in the preheatingchamber 22 can be preheated to a predetermined temperature of 500° C. ormore (e.g., 800° C.). That is, preheating can be achieved without aheater in the preheating chamber 22, and the configuration of thepreheating chamber 22 can be simplified.

The preheat treatment described above is performed in a predeterminedtime, and then, the cylinder 29 is driven to lift the support 28.Consequently, the object passes through the through hole 55 from belowand moves into the main heating chamber 21. As a result, a main heattreatment starts immediately, and the temperature of the object in themain heating chamber 21 can be rapidly increased to a predeterminedtemperature (about 1900° C.).

As illustrated in FIG. 3, the TaC container 2 is a fitted containerincluding an upper container 2 a and a lower container 2 b that can befitted to each other. With this configuration, although the internalspace of the TaC container 2 is sealed, a small amount of gas atoms canmove from the inside of the TaC container 2 to the outside (or in theopposite direction). In addition, the TaC container 2 is configured toexert C-atom adsorption ion pump function described later in the case ofperforming a high-temperature treatment under vacuum. Specifically, theTaC container 2 is made of a tantalum metal and is configured to exposea tantalum carbide layer in the internal space.

More specifically, the TaC container 2 is configured such that a TaClayer is formed as the innermost layer (layer closest to the object), aTa₂C layer is formed outside the TaC layer, and a tantalum metal as abase material is formed outside the Ta₂C layer. Thus, as long as thehigh-temperature treatment continues under vacuum as described above,the TaC container 2 shows the function of continuously adsorbing carbonatoms from a surface of the tantalum carbide layer and taking the carbonatoms therein. In this regard, the TaC container 2 of this embodimenthas the C-atom adsorption ion pump function (ion getter function). Theinnermost TaC layer is supplemented with Si. Accordingly, in the heattreatment, Si supplemented to this TaC layer is sublimated, and Si vaporis generated. In Si vapor and C vapor contained in the atmosphere in theTaC container 2, only the C vapor is selectively occluded in the TaCcontainer 2, and thus, the atmosphere in the TaC container 2 can bemaintained as a high-purity Si atmosphere.

A source of Si is not limited to the structure that supplies Si to aninner wall of the TaC container 2, and the inner wall of the TaCcontainer 2 may be made of Ta_(x)Si_(y) (e.g., TaSi₂ or Ta₅Si₃) or otherSi compounds, for example. Alternatively, solid Si (Si pellet) may bedisposed in the TaC container 2.

The SiC container 3 is configured to include polycrystalline SiC such as3C-SiC. In this embodiment, the entire SiC container 3 is constituted bySiC. A part (e.g., inner surface) of the SiC container 3 may be made ofpolycrystalline SiC as long as Si vapor and C vapor are generated in theinternal space during the heat treatment.

The SiC container 3 is a fitted container including an upper container 3a and a lower container 3 b that can be fitted to each other, in thesame manner as the TaC container 2. With this configuration, althoughthe internal space of the SiC container 3 is sealed, a small amount ofgas atoms can move from the inside of the SiC container 3 to the outside(or in the opposite direction). Accordingly, Si vapor generated in theTaC container 2 moves from the outside of the SiC container 3 to theinside of the SiC container 3 so that Si vapor can be supplied to theinternal space of the SiC container 3. As illustrated in FIG. 3, sincethe SiC container 3 is placed in the TaC container 2, the SiC container3 is smaller in size than the TaC container 2. The SiC container 3houses at least one underlying substrate 40.

The underlying substrate 40 is a substrate serving as a base or anunderlying layer for forming an epitaxial layer 41. The underlyingsubstrate 40 may be a SiC substrate or may be a substrate of a materialexcept SiC (e.g., an Al compound or a N compound). In the case of theSiC substrate, crystalline polymorphism is optional, and may be 3C-SiC,4H-SiC, or 6H-SiC, for example. In a case where the underlying substrate40 is a SiC substrate, the off-angle (see FIG. 5) relative to the<11-20> direction or the <1-100> direction may be 1° or less or largerthan 1°. The epitaxial layer 41 may be formed on any one of the Sisurface and the C surface of the underlying substrate 40.

Next, an epitaxial growth step will be described. In this embodiment,the epitaxial layer 41 of single crystalline 3C-SiC is formed on theunderlying substrate 40 by a vapor-phase epitaxial growth method.Specifically, as illustrated in FIG. 3, the underlying substrate 40 ishoused in the SiC container 3, and the SiC container 3 is further housedin the TaC container 2. A temperature gradient is provided in such amanner that the temperature in an upper portion of the TaC container 2(where the epitaxial layer 41 is formed) is high. The temperaturegradient is preferably 2° C./mm or less, and more preferably about 1°C./mm. In this state, the TaC container 2 is heated at a temperature of1600° C. or more and 2300° C. or less.

With this heat treatment, Si supplied to the inner surface of the TaCcontainer 2 is sublimated, and the inside of the TaC container 2 has anequilibrium vapor pressure of Si. In the case of using another Sisource, sublimation of Si makes the inside of the TaC container 2 at anequilibrium vapor pressure of Si. Accordingly, the SiC container 3 isheated at high temperatures under a Si vapor pressure, and thus, the SiCcontainer 3 is subjected to etching (Si vapor pressure etching).Specifically, the following reaction is performed. To put it briefly, byheating SiC under a Si vapor pressure, SiC is sublimated as Si₂C orSiC₂, for example, through thermal decomposition and chemical reactionwith Si. In the SiC container 3, a high C partial pressure is generated,and the C component is transferred to the surface of the underlyingsubstrate 40 using a temperature gradient of 2° C./mm or less as adriving force, and 3C-SiC is crystallized.

The SiC container 3 is subjected to Si vapor pressure etching so thatcarbonization of the SiC container 3 can be prevented and C atoms (orthe C compound) can be sublimated from the SiC container 3. Here, sincethe TaC container 2 has the C-atom adsorption ion pump function asdescribed above, the space inside the TaC container 2 and outside theSiC container 3 has a high-purity Si atmosphere. On the other hand, Catoms are not absorbed in the inside of the SiC container 3, and thus,the inside of the SiC container 3 has a C atmosphere. In addition, Sivapor generated from the Si source of the TaC container 2 also entersthe inside of the SiC container 3 through a gap between the uppercontainer 3 a and the lower container 3 b of the SiC container 3.Accordingly, the inside of the SiC container 3 has a Si+C atmosphere.Thus, by performing the heat treatment with a temperature gradient, theepitaxial layer 41 of single crystalline 3C-SiC can be formed on thesurface of the underlying substrate 40 (epitaxial layer growth step). Inthis manner, a substrate with the epitaxial layer can be produced.

With reference to FIG. 4, molecular sequences of 4H-SiC and 3C-SiC willbe briefly described. As illustrated in FIG. 4(a), 3C-SiC is configuredsuch that Si atoms and C atoms are stacked, and a monomolecular layer ofSi and C has a height of 0.25 nm. In 4H-SiC, the direction of sequenceis reversed at every two molecular layers as illustrated FIG. 4(b),whereas in 3C-SiC, the direction of sequence is not reversed and isuniform.

Here, the underlying substrate 40 is covered with the TaC container 2and the SiC container 3 as described above so that the partial pressureof C vapor in the SiC container 3 can be increased. Thus, even with atemperature gradient of about 1° C./mm, the epitaxial layer 41 isallowed to grow sufficiently. In a known sublimation technique or othertechniques, a wider range of temperature gradient is necessary forobtaining an effective growth velocity. To increase the range oftemperature gradient, however, a precise heater and fine control areneeded, which leads to an increase in manufacturing costs. In view ofthis, this embodiment only requires that the temperature gradient be 2°C./mm or less, about 1° C./mm, or 1° C./mm or less, and thus,manufacturing costs can be reduced.

By causing the epitaxial layer 41 to grow with the technique of thisembodiment, the epitaxial layer 41 of single crystalline 3C-SiC can beformed even using an underlying substrate 40 of a material except SiC.The epitaxial layer 41 of single crystalline 3C-SiC can also be formedusing an underlying substrate 40 of a material except 3C-SiC. Inaddition, SiC can grow on 4H-SiC using an MBE (molecular beam epitaxy)technique and a CVD (chemical vapor deposition) technique. The MBEtechnique and the CVD technique, however, are not suitable for a heattreatment at 1600° C. or more, for example, and thus, the growthvelocity has an upper limit. On the other hand, a sublimation proximitymethod is expected to have a high growth temperature and a high growthvelocity, but has poor uniformity in a substrate surface. On the otherhand, the method of this embodiment is suitable for a heat treatment athigh temperatures of 1600° C. or more, and epitaxial growth of SiC isperformed in a semi-closed system of the Poly-SiC container, and thus,has high uniformity.

In a case where the off-angle of the SiC substrate is large (e.g.,larger than 1°), step flow growth occurs so that crystallinepolymorphism of the underlying substrate 40 can be easily propagated.Thus, 4H-SiC as the epitaxial layer 41 grows on 4H-SiC as the underlyingsubstrate 40. Thus, in a case where the epitaxial layer 41 of the 3C-SiCis needed, the off-angle of the SiC substrate is preferably small (e.g.,1° or less).

Next, an experiment for determining advantages in housing the SiCcontainer 3 in the TaC container 2 will be described with reference toFIGS. 6 and 7. As illustrated in FIG. 6, in this experiment, the SiCcontainers 3 were placed inside and outside the TaC container 2, and theepitaxial layer 41 was caused to grow on the underlying substrate 40 ineach SiC container 3.

FIG. 7 shows results of this experiment. FIG. 7(a) is a micrograph ofthe Si surface and the C surface of the epitaxial layer 41 in the caseof epitaxial growth performed by placing the SiC container 3 outside theTaC container 2. FIG. 7(b) is a micrograph of the Si surface and the Csurface of the epitaxial layer 41 in the case of epitaxial growthperformed by placing the SiC container 3 inside the TaC container 2. Bydisposing the SiC container 3 inside the TaC container 2 in this manner,the surface of the epitaxial layer 41 is planalized, thereby forming ahigh-quality epitaxial layer 41. The growth velocity also increasesabout five times in the case of disposing the SiC container 3 inside theTaC container 2. By covering the underlying substrate 40 with the SiCcontainer 3 and the TaC container 2 in the manner described above, thehigh-quality epitaxial layer 41 can be formed at high speed.

Thereafter, an experiment for confirming uniform formation of theepitaxial layer 41 irrespective of the position in the SiC container 3will be described with reference to FIGS. 8 and 9. As illustrated inFIG. 8, in this experiment, the underlying substrate 40 was placed invarious environments, and heated at 1800° C. with a temperature gradientof about 1° C./mm to compare the amount of growth of the epitaxial layer41. In particular, the experiment was conducted with variations of adistance L from the surface of the underlying substrate 40 to thematerial (the SiC container 3 or a polycrystalline SiC plate 45). InFIGS. 8(a) and 8(b), one underlying substrate 40 is housed in one SiCcontainer 3, whereas in FIGS. 8(c) and 8(d), two underlying substrates40 are housed in one SiC container 3. Although FIG. 8 does not show theTaC container 2, each SiC container 3 is housed in the TaC container 2.

FIG. 9 shows results of this experiment. FIG. 9 is a graph showing acorrespondence between a distance L from the surface of the underlyingsubstrate 40 to a material and a growth velocity of the epitaxial layer41 formed on the underlying substrate 40 in each of the underlyingsubstrates 40 used in FIGS. 8(a) through 8(d). As shown in FIG. 9, allthe underlying substrates 40 have substantially the same growthvelocity. Thus, it was confirmed that if the temperature gradient isuniform, the epitaxial layer 41 is uniformly formed independently of theposition in the SiC container 3. As illustrated in FIGS. 8(c) and 8(d),by housing the plurality of underlying substrates 40 in one SiCcontainer 3, the epitaxial layer 41 can be efficiently formed.

As illustrated in FIG. 9, the growth velocity of the epitaxial layer 41is 6 to 8 μm/h at 1800° C., which is six to eight times as high as thatin the CVD method of PTL 1. In the method of this embodiment, theheating temperature can be 1800° C. or more, and thus, a higher growthvelocity can be achieved. The temperature gradient may be furtherincreased to be higher than 1° C./mm. This can achieve a higher growthvelocity.

The TaC container 2 of this embodiment can be used not only for theprocess of forming the epitaxial layer 41 but also for the process ofetching the underlying substrate 40 (SiC substrate). As described above,since the inside of the TaC container 2 can be maintained in ahigh-purity Si atmosphere, as illustrated in FIG. 10, a SiC substratedirectly (without interposition of the SiC container 3) disposed in theTaC container 2 can be etched by heating at 1600° C. or more (the Sivapor pressure etching).

The etching step may be performed at any time, and may be performed inorder to planarize a SiC substrate after being cut out from an ingot andsubjected to mechanical polishing (i.e., before formation of theepitaxial layer 41) or in order to planarize the epitaxial layer 41roughened by injection of ions (impurity) (i.e., after formation of theepitaxial layer 41), for example.

In the above-described process, vapor-phase epitaxial growth isperformed with the SiC container 3 housed in the TaC container 2 and theunderlying substrate 40 housed in the SiC container 3 so that singlecrystalline 3C-SiC is caused to grow as the epitaxial layer 41 on theunderlying substrate 40. With a similar process, single crystal 4H-SiCor single crystal 6H-SiC, for example, can be caused to grow as anepitaxial layer 41 on the underlying substrate 40. Crystallinepolymorphism of the epitaxial layer 41 to grow can be selected bychanging the off-angle and the temperature, for example, of theunderlying substrate 40.

FIG. 11 illustrates an embodiment in which a plurality of underlyingsubstrates 40 are housed in one SiC container 3 that is housed in a TaCcontainer 2. As described above, since the epitaxial layers 41 of singlecrystalline 3C-SiC having similar growth velocities and qualities can beformed independently of the position of the SiC container 3 by using themethod of an aspect of the present invention, substrates with theepitaxial layers 41 can be efficiently formed.

As described above, in this embodiment, in a state in which the SiCcontainer 3 of a material including polycrystalline SiC is housed in theTaC container 2 of a material including TaC and the underlyingsubstrates 40 are housed in this SiC container 3, the TaC container 2 isheated with a temperature gradient in such a manner that the inside ofthe TaC container 2 is at a Si vapor pressure. Consequently, C atomssublimated by etching of the inner surface of the SiC container 3 arebonded to Si atoms in an atmosphere in the SiC container 3, and thereby,the epitaxial layers 41 of single crystalline SiC (e.g., 3C-SiC, 4H-SiC,or 6H-SiC) grows on the underlying substrates 40.

Accordingly, a high-purity epitaxial layer 41 of single crystalline SiCcan be formed at high velocity. In addition, since the material for theepitaxial layers 41 is the SiC container 3, the epitaxial layers 41 areallowed to grow uniformly, as compared to, for example, CVD in which asource gas is introduced.

In the vapor-phase epitaxial growth method of this embodiment, amaterial for the underlying substrate 40 may be an Al compound or a Ncompound, a material for the epitaxial layer 41 may be SiC, and anoff-angle to the <11-20> direction or the <1-100> direction may be 1° orless.

Accordingly, with the method of an aspect of the present invention, theunderlying substrate 40 is not limited to SiC, and thus, a versatileepitaxial growth method can be achieved. As a result, in a case wherethe underlying substrate 40 is SiC and the off-angle is small, a terraceexpands, and a high-quality epitaxial layer of single crystalline SiCcan be easily formed independently of crystalline polymorphism of theunderlying substrate 40.

In the vapor-phase epitaxial growth method of this embodiment, thetemperature gradient is preferably 2° C./mm or less.

Thus, with the method of an aspect of the present invention, thepressure of C atoms in the SiC container 3 is increased, and thus, anepitaxial layer is allowed to grow sufficiently even with a smalltemperature difference as described above. As a result, the heater andheating control can be simplified.

In the vapor-phase epitaxial growth method of this embodiment, theplurality of underlying substrates 40 are placed in the SiC container 3and the epitaxial layer 41 is caused to grow on each of the plurality ofunderlying substrates 40.

Accordingly, the epitaxial layers 41 can be formed at the same time onthe plurality of underlying substrates 40, and therefore the process canbe performed efficiently. In particular, the use of the method of theaspect of the present invention enables the epitaxial layer 41 to beformed uniformly independently of the position in the SiC container 3,and thus, quality does not degrade.

In the vapor-phase epitaxial growth method of this embodiment, the innersurface of the TaC container 2 is made of Si or a Si compound, and Siatoms are sublimated from the inner surface of the TaC container 2 byheating during growth of the epitaxial layer 41 so that the inside ofthe TaC container 2 is at a Si vapor pressure.

Accordingly, a labor of an operator can be alleviated, as compared to amethod of placing solid Si or the like in the TaC container 2. Inaddition, by forming Si or the like over a wide range of the innersurface of TaC, a uniform Si atmosphere can be obtained.

The foregoing description is directed to a preferred embodiment of thepresent invention, and the configuration described above may be changed,for example, as follows.

The shapes of the TaC container 2 and the SiC container 3 describedabove are examples, and may be changed as appropriate. For example, theTaC container 2 and the SiC container 3 may have different shapes or mayhave the same (analogous) shape. As illustrated in FIG. 8(d), the TaCcontainer 2 or the SiC container 3 may have a plurality of spaces. OneTaC container 2 may house a plurality of SiC containers 3, and each ofthe SiC containers 3 may house a plurality of underlying substrates 40so that the epitaxial layers 41 can be formed thereon.

For example, to control the amount of growth of the epitaxial layer 41accurately, an inert gas (e.g., an Ar gas) may be introduced duringformation of the epitaxial layer 41 to reduce the growth velocity of theepitaxial layer 41.

Atmospheres of the internal space of the TaC container 2 and theinternal space of the SiC container 3 (especially partial pressures ofSi and C) vary depending on the amount of the Si source, the degree ofcarbon adsorption function of TaC, the volume of the TaC container 2,the volume of the SiC container 3, and so forth. Thus, by making thesefactors different from one another, the growth velocity and quality, forexample, of the epitaxial layer 41 can be controlled.

REFERENCE SIGNS LIST

-   -   2 TaC container    -   2 a upper container    -   2 b lower container    -   3 SiC container    -   3 a upper container    -   3 b lower container    -   11 high-temperature vacuum furnace    -   40 SiC substrate    -   41 epitaxial layer    -   45 polycrystalline SiC plate

1. A manufacturing device of SiC semiconductor substrates, the devicecomprising: a SiC container in which Si vapor and C vapor are generatedin the internal space during the heat treatment; and a high-temperaturevacuum furnace capable of heating the SiC container in Si atmosphere. 2.The manufacturing device of SiC semiconductor substrates according toclaim 1, wherein the SiC container is housed in Si atmosphere and anunderlying substrate is housed in the SiC container.
 3. Themanufacturing device of SiC semiconductor substrates according to claim1, wherein the high-temperature vacuum furnace is capable of heatingwith a temperature gradient.
 4. The manufacturing device of SiCsemiconductor substrates according to claim 1, the device furthercomprising: a TaC container in which Si vapor is generated in theinternal space during the heat treatment.
 5. The manufacturing device ofSiC semiconductor substrates according to claim 4, wherein the SiCcontainer is housed in the TaC container.
 6. A manufacturing device ofSiC semiconductor substrates, the device comprising: a SiC container inwhich Si vapor and C vapor are generated in the internal space duringthe heat treatment; and a TaC container in which Si vapor is generatedin the internal space during the heat treatment.
 7. The manufacturingdevice of SiC semiconductor substrates according to claim 6, wherein theSiC container is housed in TaC container and an underlying substrate ishoused in the SiC container.
 8. The manufacturing device of SiCsemiconductor substrates according to claim 4, wherein the TaC containerincludes a TaC layer and a source of Si.
 9. The manufacturing device ofSiC semiconductor substrates according to claim 1, wherein the SiCcontainer is configured to include polycrystalline SiC.
 10. Themanufacturing device of SiC semiconductor substrates according to claim1, wherein the underlying substrate comprises a plurality of underlyingsubstrates, and the plurality of underlying substrates are placed in theSiC container.